Seed germination is the biological process where an embryo within a seed resumes growth and develops into a seedling. Measuring this process is important for assessing the quality and viability of a seed lot, allowing growers to predict field success. Quantifying how many seeds sprout and how quickly they do so informs decisions about planting rates and seed storage conditions.
Standardizing the Germination Test
Obtaining reliable germination data requires standardized testing conditions. The first step involves selecting a statistically relevant sample size, typically 50 or 100 seeds, to represent the entire seed lot. This random sample is planted on a neutral, standardized substrate like blotter paper, sand, or sterilized peat moss, ensuring consistent contact with moisture.
The chosen medium must be kept moist but never saturated, as too much water can deprive the seeds of necessary oxygen and encourage fungal growth. Environmental factors must be strictly controlled, including maintaining a consistent temperature, often within the range of 70°F to 80°F for many vegetable seeds. For many species, specific light and dark cycles or alternating temperature regimes are required to break dormancy and promote optimal sprouting. A seed is counted as “germinated” when the radicle, or primary root, visibly emerges from the seed coat.
Calculating Germination Percentage
Germination Percentage (GP) is the simplest measure, indicating the total viability of the seed lot regardless of the time it took to sprout. It is calculated after a species-specific standard period, which can range from three to five days for fast-sprouting seeds to 14 days for slower varieties. The formula is: \(\text{GP} = (\text{Number of Seeds Germinated} / \text{Total Number of Seeds Planted}) \times 100\).
For example, if 88 seeds out of 100 planted sprout, the germination percentage is 88%. This number directly translates to the expected success rate in the field. A germination percentage of 80% or higher is considered excellent for commercial quality seeds. If the resulting percentage is lower than desired, the grower must increase the seeding rate to compensate for the non-viable portion, ensuring the correct density of plants in the field.
Measuring Germination Speed
While the final percentage determines the success of the seed lot, germination speed measures the vigor at which that success is achieved. A faster, more uniform rate of germination often leads to stronger, more competitive seedlings that are better able to resist disease and environmental stresses. To measure this, daily monitoring and counting of newly germinated seeds are required throughout the test period.
A widely used metric for quantifying speed is the Mean Germination Time (MGT), which calculates the average time it takes for a seed in the sample to sprout. MGT is a weighted average that factors in both the number of seeds that germinate and the time interval at which they do so. The calculation involves multiplying the number of seeds that germinated each day by the day number, summing these products, and dividing the total by the final number of seeds that germinated.
A lower MGT value signifies quicker and more vigorous germination, which is a desirable trait for a seed lot. For instance, two seed lots may both achieve an 85% final germination percentage, but the lot with a lower MGT will produce seedlings that emerge more uniformly and establish themselves faster. By tracking both the final percentage and the speed of germination, one gains a comprehensive understanding of the seed lot’s quality.